Monday, August 18, 2008

Handheld gadget offers a window on Rome's past

Visitors to Rome will no longer have to rely on their imagination to see the ancient city at its glorious peak. Just point TimeMachine, a new handheld gadget produced by Ducati Myers and the University of Bologna, at famous sites like the Colosseum and it automatically displays a 3D reconstruction of the building.

The device is the first commercial application of the Rome Reborn project, an ongoing effort to reconstruct the city as it was in AD 320. The starting point of the project was an impressively detailed physical model of the city, some 15 meters across, built over a 40 years span in the twentieth century. That model was laser-scanned and digitised by an international team of researchers led by Bernard Frischer at the University of Virginia. The latest version, Rome Reborn 2.0, was unveiled at the SIGGRAPH conference in LA last week.

Fun though it is to fly over the ancient city and zoom in on specific buildings, it's when those flashy graphics meet present day Rome that Rome Reborn becomes most gripping.

That's where TimeMachine comes in. Point the device at a ruin and it displays the picture on a small screen. The gadget then uses image recognition to identify the delapidated buildin , and superimposes the virtual reconstruction of its heyday on top. You can then walk towards, or around the building to see the virtual reconstruction from any view. The viewer is given a moveable window on the past.

It's even relatively cheap to use - hiring the device costs around 5 Euros per hour, according to Joel Myers. So far TimeMachine is active at the Colosseum, and a version designed for the Forum should be available next month.

Thursday, August 14, 2008

Just an illusion: still images that move

Earlier this week I found myself on a long-haul flight to the SIGGRAPH computer graphics conference in Los Angeles. To pass the time I decided to catch up on some of the papers that are being presented here. But I had to stop when it came to the mind-warping, travel-sickness-inducing images that littered a paper by researchers from National Cheng Kung University in Taiwan and the Chinese University of Hong Kong.

Ming-Te Chi and colleagues have analysed a number of hand drawn examples of these 'self-animating images', such as the image above - "Rotating Snake" by Akiyoshi Kitaoka. Even though the viewer knows they are static the images unnervingly seem to move anyway. Chi's team is trying to find out why.

They've identified a number of important factors. The pictures appear to creep because of the arrangement of colour bands in the small repeated asymmetric patterns (dubbed RAPs). Certain combinations seem to give the impression of it creeping in a particular direction, although that effect is relatively weak. The illusion is strengthened if a ribbon of RAPs that appears to flow to the right is placed next to one that appears to flow to the left.

Most impressively, Chi's team has worked out a way to predict which colour combinations give the best illusions. By plotting the four colours used in their images on a standard colour wheel they found a characteristic pattern emerged: the four colours used should always be as different from each other as is possible.

White couples best with black, blue works well with yellow. With that discovery the researchers could begin experimenting with a wider palette of colours than was previously available to produce self-animating images. As a result they can make far more sophisticated images.